There are 3 main credit agencies: Experian, Equifax, and TransUnion. Some banks check only one agency, others merge the three and take an average. Just so you know, 640 is not the greatest score. You'll definitely pay more interest. I think 680+ is good and 700+ is considered "A" paper credit.
At the least, you should pull your credit reports and verify all the information as accurate. Sometimes, people have been the victim of identity theft and don't even know it. Your credit report might reveal this. Simply check the accounts and make sure they are all accurate. That's the best place to start. For more resources, click my post above. Good luck to you.